1. Field of the Invention
This invention relates to a signal conditioner which operates on fixed rise time, pulse-amplitude modulated carriers as is found at the last IF stage of a TACAN receiver, and, in particular, to apparatus that determines the time of arrival of the 50% leading edge amplitude point of a pulse-amplitude modulated carrier without introducing any delay and before conventional video detection smearing. A second part of the apparatus uniquely performs two additional functions, that of video detection, and that of sampling and holding the peak amplitude of the pulse-amplitude modulated carrier for subsequent analog to digital conversion and digital signal processing. Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
2. Description of the Prior Art.
Several technical disadvantages of prior-art leading edge 50% point time of arrival detection schemes of fixed rise-time pulse-amplitude modulated carriers are:
First, conventional approaches introduce a fixed lag in outputting the 50% point time of arrival signal. The minimum lag in the conventional approach is usually equal to one-half the rise time of the envelope of the pulse, that is, the 50% point time of arrival can not be outputted until the peak of the pulse is first determined.
Secondly, important information, the carrier is stripped away via a video detector which effectively introduces smearing and degradation.
Thirdly, the leading edge of a video detected carrier has an infinite number of slopes depending on the magnitude of the amplitude of the pulse modulation causing dc off-set voltages of comparators to introduce different 50% point leading-edge timing errors as a function of slope, i.e., pule amplitude.
Prior to this invention, all front ends (or signal conditioners), to applicant's knowledge, operated in the analog domain, that is, historically, utilizing electro-mechanical servos or analog and phased locked loops. Prior art devices were not concerned with digitizing the signal, but, instead, were concerned with operation in the analog domain.